LAUSANNE, Switzerland, Feb. 3 (UPI) -- Marijuana use appears to have decreased among most European and North American adolescents from 2002 to 2006, researchers in Switzerland said.

Emmanuel Kuntsche of the Swiss Institute for the Prevention of Alcohol and Drug Problems in Lausanne, Switzerland, and colleagues analyzed data from 93,297 15-year-old students who participated in the Health Behavior in School-Aged Children study.

Study participants from 31 countries -- mostly in Europe and North America -- were surveyed in 2002 and again in 2006 about marijuana use and the number of evenings per week they usually spend out with their friends, among other topics.

The study, published in the Archives of Pediatrics & Adolescent Medicine, found marijuana use decreased in most countries, with the most significant declines in England, Portugal, Switzerland, Slovenia and Canada. Increases were observed in Estonia, Lithuania, and Malta and among girls in Russian.

In addition, the number of evenings out with friends also declined in most countries, although there was a wide range in averages, from about one evening per week for Portuguese girls to more than three evenings per week among boys and girls in the Ukraine, Russia, Scotland, Estonia and Spain.

"The more frequently adolescents reported going out with their friends in the evenings, the more likely they were to report using cannabis, or marijuana," the study authors said in a statement.